This application claims the entire benefit of Japanese Patent Application Number 2009-154175 filed on Jun. 29, 2009, the entirety of which is incorporated by reference.
1. Field of the Invention
The present invention relates to a structure for attaching a motor assembly comprising a commutator motor and a brush holder unit to a tubular housing such as used for a power tool.
2. Description of Related Art
As disclosed in Japanese Laid-open Patent Publication No. 2007-143314, a power tool such as an electric hammer has a tubular housing, and a stator of a commutator motor (e.g., universal motor) is accommodated in the housing, while a rotor of the commutator motor is rotatably supported by a bearing provided in the housing. Attached to the housing adjacent to the commutator motor is a brush holder unit which holds brushes being slidable in contact with a commutator provided on the rotor.
FIG. 9 is a perspective view of a motor housing 30 to which a motor assembly is attached, FIG. 10 is a vertical section taken in a right and left direction, and FIG. 11 is a vertical section taken in a front and rear direction. As seen in the drawings, a bearing 31 for rotatably supporting a rotor (not shown) of a commutator motor is protrusively provided at a lower end of a tubular motor housing 30. The motor housing 30 is open at an upper end thereof. The motor housing 30 has an attachment seat 32 peripherally around the bearing 31, and a disk-shaped brush holder unit 35 for holding a pair of brushes 36, 36 each being slidable in contact with a commutator segment of a commutator provided on the rotor is mounted to the attachment seat 32 and fixed by screwing bolts from beneath the brush holder unit 35. In the meantime, an accommodating portion 33 for the commutator motor is formed in the motor housing 30, and bosses 34, 34 are provided at the bottom of the accommodating portion 33, against which an end surface of a stator 37 is in contact and fixed by screws.
Therefore, when the brush holder unit 35 and the stator 37 are attached to the motor housing 30, as seen in FIGS. 12 and 13, the brush holder unit 35 is fixed to the attachment seat 32 by screws 38, 38 from beneath the motor housing 30. On the contrary, the stator 37 is inserted into the accommodating portion 33 from above the motor housing 30 and fixed to the bosses 34, 34 by screws 39, 39.
As described above, the brush holder unit 35 and the stator 37 are mounted from the opposite sides and fixed to the motor housing 30 by screws. This disadvantageously leads to deterioration of workability during assembly, an increased diameter of the stator 37 because of proving screw-threaded portions, and possible limitations on the construction of the brush holder unit 35.
Further, since the bearing 31 of the rotor is protrusively provided in the motor housing 30 at the middle of the attachment seat 32 of the brush holder unit 35, a sufficient bearing rigidity is not obtained so that the operating life of the brushes 36, 36 may be decreased due to vibration of the rotor.
It is thus an object of the present invention to provide an attachment structure for a motor assembly, by which a motor assembly comprising a commutator motor and a brush holder unit can be assembled with better workability, and by which an enhanced bearing rigidity can be obtained to ensure a sufficient operating life of the brushes, while avoiding increased diameter of the stator and possible limitations on the construction of the brush holder unit.